The present invention relates to processes for the production of polymers, and more specifically, to a process for producing carbo-chain homopolymers, block- and random copolymers of conjugated dienes with vinylaromatic monomers; the resulting polymers are employed as a material for the manufacture of tyres, rubber-engineering articles, rubber footwear. Articles manufactured from such polymers are not inferior to articles made of natural rubber in respect of their cracking-resistance and heat-formation.
Carbo-chain block- and random copolymers can be used in the production of cables owing to their high dielectric properties.
A process is known in the art for producing carbo-chain homopolymers, block- and random copolymers by polymerization of conjugated dienes, vinyl- or divinylaromatic monomers or intercopolymerization thereof in an inert hydrocarbon solvent medium at a temperature within the range of from -30.degree. to 150.degree. C. in the presence of an organolithium catalyst and a modifying additive, i.e. a compound of the general formula R--(OM).sub.n, wherein n is an integer of from 1 to 3, M is potassium, sodium, rubidium or cesium; R is an aliphatic, aromatic or a cycloaliphatic radical.
This prior art process has the disadvantage that the organic compounds of alkali metals containing at most 20 carbon atoms are employed as the modifying additive and these compounds are but sparingly soluble in aliphatic, cycloaliphatic and aromatic hydrocarbons. In the practice of this process it is necessary to disperse these insoluble products, which is accompanied by difficulties in storage and the precise metering of the resulting suspensions into the reaction medium. By-products formed with the use of oxygen-containing organic compounds of alkali metals with a number of carbon atoms below 20 are volatile and can contaminate the recycle solvent thus necessitating additional investments for its purification. Furthermore, the polymerizate is unstable and, to prevent destruction of the resulting polymer upon recovery and drying thereof, stabilizing agents should be introduced thereinto. All this complicates the polymerization process technology.
A process is also known in the art for producing carbo-chain random copolymers of conjugated dienes with vinylaromatic monomers in a hydrocarbon solvent.
The process is conducted at a temperature within the range of from -30.degree. to 150.degree. C. in the presence of a catalyst comprising a compound of the general formula R(Li).sub.x, wherein R is a hydrocarbon radical containing 1 to 20 carbon atoms, x is an integer of from 1 to 4, and in the presence of an additive comprising an organometallic compound. Such compounds can be those corresponding to formulae: R'M, R'(yM).sub.n ; R"(C-yM).sub.n and the like, wherein R' is a hydrocarbon radical with 1 to 20 carbon atoms, R" is a hydrocarbon radical with 4 to 20 carbon atoms, y is an atom of oxygen or sulphur; n is an integer of from 1 to 3, and M is sodium, potassium, rubidium or cesium.
As a solvent for the copolymerization use is made of aliphatic, aromatic and cycloaliphatic hydrocarbons. As a result, a solution of a copolymer is obtained, which is then added with an antioxidant. Afterwards, the desired product is recovered by conventional methods (cf. British Pat. No. 1,029,445).
This prior art process has disadvantages for example, the organic compounds of alkali metals corresponding to the above-given formulae are sparingly soluble in aliphatic, cycloaliphatic and aromatic hydrocarbons. In the practical implementation of this process it is necessary to form suspensions of these insoluble products. Furthermore difficulties are encountered in storage and the precise metering of the dispersion prior to admission thereof into the reaction system, especially in performing a continuous polymerization process.
The resulting polymerizate is unstable and, to prevent the polymer destruction upon recovery and drying thereof, a stabilizing agent must be added.
Furthermore, in the case of using, as modifying additives, oxygen- and sulphur-containing organic compounds of alkali metals volatile organic by-products are liberated which can contaminate the recycle solvent, thus necessitating additional expenses for purification thereof.
A, apart from the above-discussed processes, a process is known in the art for producing carbo-chain random copolymers of conjugated dienes with vinylaromatic monomers (cf. British Pat. No. 1,501,136) comprising copolymerization of conjugated dienes with vinylaromatic monomers in a hydrocarbon solvent medium at a temperature within the range of from -30.degree. to 150.degree. C. in the presence of a catalyst, i.e. lithium or an organolithium compound of the general formula R(Li).sub.x, wherein R is a hydrocarbon radical, x is an integer of from 1 to 4, in the presence of a modifying additive comprising a reaction product of alkali metals Na, K, Rb, Cs or hydroxides thereof with conjugated diene homopolymers or copolymers with terminal hydroxy groups having molecular weight of from 500 to 5,000 or compounds of the general formula R.sub.1 (M).sub.y, wherein ##STR2## wherein n is an integer of from 1 to 5; m is an integer of from 4 to 100, M is the alkali metals mentioned hereinbefore, y is an integer of 1 to 10; said additives being taken in an amount ranging from 0.005 to 2.5 moles per one mole of active lithium.
This prior art process has a disadvantage residing in instability of the polymerization product due to the fact that the modifying additive employed does not prevent the oxidation of the polymer.